Lithographic apparatus and device manufacturing method

ABSTRACT

In an immersion lithographic apparatus, bubble formation in immersion liquid is reduced or prevented by reducing a gap size or area on a substrate table and/or covering the gap.

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/980,406 filed Dec. 29, 2010, which is a continuation ofco-pending U.S. patent application Ser. No. 11/603,228 filed Nov. 22,2006, now allowed, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/285,774 filed Nov. 23, 2005, now U.S. Pat. No.7,633,073, the entire contents of each of the foregoing applications ishereby incorporated by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication WO 99/49504, hereby incorporated in its entirety byreference. As illustrated in FIGS. 2 and 3, liquid is supplied by atleast one inlet IN onto the substrate, preferably along the direction ofmovement of the substrate relative to the final element, and is removedby at least one outlet OUT after having passed under the projectionsystem. That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 2 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-andout-lets positioned around the final element are possible, one exampleis illustrated in FIG. 3 in which four sets of an inlet with an outleton either side are provided in a regular pattern around the finalelement.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another solution which has been proposed is to provide the liquid supplysystem with a barrier member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table, as depicted in FIG. 5. The barrier member issubstantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis). A seal is formed between the barriermember and the surface of the substrate. In an embodiment, the seal is acontactless seal such as a gas seal. Such a system with a gas seal isdisclosed in U.S. patent application publication no. US 2004-0207824,hereby incorporated in its entirety by reference.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting the substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus may have only one table movable between exposure andmeasurement positions.

One of the problems with immersion lithography is the presence ofbubbles in the immersion liquid. If the path of the projection beampasses through areas of immersion liquid that contain bubbles, this maydeleteriously affect the quality of the patterned imaged projected ontothe substrate.

Bubbles may be present in the immersion liquid for a number of reasons.The first, for example, is that not all the gas is displaced by liquidwhen the immersion space is filled with liquid.

Macroscopic features may prevent capillary filling of the gap betweenthe immersion system and the substrate within the time it takes for thesubstrate to pass across the immersion system. This may result in gasbecoming trapped in the gap. The surface tension of the liquid pulls thetrapped gas volume into a bubble, which will float once the buoyancy ofthe bubble exceeds the surface tension of the immersion liquid holdingthe gas bubble to the a surface of the gap. The presence of a gap in awall of the immersion space may provide a trap in which a bubble of gasmay remain even when the space is immersed in liquid.

Rough surfaces may also prevent the capillary filling of the gap, but ona microscopic scale. The immersion liquid contacts the projections of arough surface, but does not fully wet the contours of the surface. Theextent of the roughness of the surface is proportional to the forcecaused by the surface tension and so gas bubbles remain trapped moreeasily. As the immersion liquid layer passes over the rough surface, the“effective contact angle” or the angle at which the liquid meets thesurface varies more than with a smooth surface, and so gas is morelikely to be trapped where the contact angle is decreased, i.e., wherethe distal part of projections on the surface meet the liquid before theproximal part of the projection, leaving a corner of gas at the upstreamproximal part of the projection.

Secondly, for example, bubbles may form spontaneously because of achange in temperature or energy or other factors. Alternatively oradditionally, gas (e.g., air) may be sucked into the system if thepressure of the system falls, e.g. with a fall in temperature. Resistsand other chemicals used on the surface of substrates may cause foamingor react with the immersion liquid or radiation, causing a change intemperature or energy, or create gas bubbles chemically.

Thirdly, for example, there may be one or more gutters configured toremove excess immersion liquid from the surface of the substrate tablethat may also trap gas when the substrate moves relative to theimmersion system or radiation system. Furthermore, these gutters maycause too much liquid to be lost, resulting in an overall drop in liquidlevel.

A way in which gas might not be replaced by liquid is depicted in FIG.11 a. Between a substrate W and a substrate table WT, for instance,there exists a gap that fills with liquid each time the gap passes underthe immersion system 12. A gas knife 15 serves to clear the path ofcontaminants and liquid for the immersion system 12. However, when theliquid-filled gap passes under the gas knife 15, liquid droplets D mayspray up onto the surface of the substrate W and the substrate table WT.Depending on the liquidphilic (e.g., hydrophilic) or liquidphobic (e.g.,hydrophobic) nature of the substrate W surface, the surface of thedroplet D forms a greater or lesser angle with the substrate surface.The liquid front F is also at an angle with the substrate W surfacebecause the substrate W surface is traveling laterally with respect tothe liquid front (the arrow indicates the direction of travel of thesubstrate table WT containing the substrate W). FIG. 10 shows therelative positions of the liquid front F and the droplet D. The meetingangles of the liquid may cause a small amount of gas to be trappedbetween the relatively moving liquid front F and droplet D surface, thuscausing a gas bubble B in the immersion liquid.

Bubbles might be formed between the substrate table and the substrate,on or around sensors or on or around a closing plate used to seal theimmersion system between scans of substrates. The bubbles might thendetach from the surfaces and float in the immersion liquid, or evenfloat up to the final optical element of the projection system, possiblyaffecting the quality of the projected image.

SUMMARY

It is desirable, for example, to reduce the presence of bubbles in partsof the immersion liquid through which the projection beam will pass.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a radiation beam,through a liquid, onto a substrate, the apparatus comprising a supporttable configured to hold an object, the object comprising (i) a sensor,or (ii) a substrate, or (iii) a closing plate, or (iv) a cover plate or(v) any combination of (i)-(iv), wherein a gap between the object andthe support table is kept to a minimum in order to minimize bubbleformation in the liquid.

There may also be provided an actuator configured to move the objectlaterally in a hole in the support table in order to reduce, when incontact with the liquid, a gap between an edge of the object and a sideof the hole.

According to an aspect of the invention, there is provided alithographic apparatus arranged to project a radiation beam, through aliquid, onto a substrate, the apparatus comprising a support tableconfigured to hold the substrate and having a plurality of objects sharea hole in the support table so as to have a common gap between them andthe hole and reduce a gap area on the support table.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a radiation beam,through a liquid, onto a substrate, the apparatus comprising a supporttable configured to hold an object, the object having a slanted surfaceand the support table having a hole, in which the object is to bepositioned, with a corresponding slanted surface to allow self-centeringof the object in the hole.

There may also be provided a cover plate to cover the object, the coverplate being segmented such that the segments are configured to slideover each other and cover a gap between the object and the supporttable.

The cover plate may be made of elastic material such that it isconfigured to stretch over the object and cover a gap between the objectand the support table. The cover plate may be a sticker configured tocover the gap, the sticker being made of glass, metal, plastic or othersuitable unreactive substance and may be adhered to the support tableand the object using a thin film of liquid (e.g., water) or the suctionof a low pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts an immersion system according to an embodiment of theinvention;

FIG. 6 depicts a plan view of a substrate table according to anembodiment of the present invention;

FIG. 7 depicts a side view of a substrate table according to anembodiment of the invention;

FIG. 8 depicts a plan view of a substrate and a cover plate according toan embodiment of the invention;

FIGS. 9 a and 9 b depict a side view of a cover plate and an objectaccording to an embodiment of the invention;

FIG. 10 depicts a side view of a bubble being formed on the surface ofthe substrate; and

FIGS. 11 a and 11 b depict an immersion system according to anembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation).

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof; as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

One way to deal with bubble formation in the immersion liquid is toprevent the formation of bubbles in the first place. This can be done bysmoothing surfaces and reducing areas in which gas bubbles can betrapped when the space is immersed in liquid.

One way of doing this is to avoid or reduce gaps in the substrate table.Gaps exist between objects that sit in holes in the substrate table andthe sides of the holes. Objects which may be placed in or on thesubstrate table include the substrate, one or more sensors and one ormore cover plates for the sensor(s) and/or the substrate. The reason forthe gaps is that the substrate and the sensors need to be or should beremovable as well as easily replaced. Therefore, there are certaintolerances that are used in order for an object in or on a substratetable to be easily removed and/or exchanged. This tolerance may be ofthe order of 0.5 mm. However, in an embodiment to reduce bubbleformation, the gap is reduced to 0.1 mm and/or the number of gaps isreduced.

One way to reduce the gap size is to use a cover plate. A cover platemay be sized so that it covers not only the object it is intended tocover, but also any gap around the object. A cover plate should have amaximum thickness no greater than a height step that the lithographicapparatus is able to accommodate.

A single cover plate may be used to cover several objects such as thesubstrate as well as one or more surrounding sensors. A gap between thesensor and a substrate is thereby covered by the cover plate. A coverplate may be integral with the object that it is intended to cover sothat as the object is dropped into a hole in the substrate table, thecover plate automatically covers not only the object but also thesurrounding hole, thereby covering up any gap. Depending on the object,the cover plate may be transparent to radiation and may be made ofquartz, for instance. The cover plate may be transparent to theradiation beam without being integral with a sensor. It may, forexample, be a pellicle that covers all or a portion of substrate tablebut is microns thick and therefore transparent to the radiation. Thepellicle may be attached to the outside of the substrate table.

The cover plate may be made in different ways. A segmented cover plateas shown in FIG. 8 may have several portions which slide relative toeach other, thereby changing shape and size and being adaptable to coverthe shapes and sizes of gaps on different substrate tables. In thiscase, the sides of the segmented plate have narrow tolerances. They arepolished to ensure that the gaps between the segments are narrow and thecontact between them is smooth. The immersion liquid offers aself-lubricating system for the segments, though stagnant liquid pocketsin a gap between segments may be avoided by extraction of the liquidfrom underneath the cover e.g. using a vacuum.

Alternatively, the cover plate may be flexible or stretchable. The coverplate may then be fixed over the object it is intended to cover and anysurrounding gap. Alternatively or additionally, the cover plate may besupplied with a stretchable hole through which an object may be insertedinto a hole in the substrate table. The stretchable hole will return toits original shape once the object is inserted, effectively closing thehole in the cover plate. FIG. 8 shows three segments of the cover plateCP around the edges of a substrate W. The different segments may each becovering a sensor on the substrate table.

The segmented cover plate should work well if there is no gap betweenthe segments. This can be facilitated, for example, by using a tenon andgroove system. It should be noted that a T-shaped gap may create morebubbles than a simple U-shaped gap and so the segments of the segmentedcover plate should be carefully linked together to avoid aggravatingbubble creation in the immersion system.

Alternatively or additionally, the cover plate or substrate or even asensor may be moved during the course of projection onto the substrate.Dynamic minimization of a gap is shown in FIGS. 9 a and 9 b and may bedependent on the location of the immersion space and projection systemwith respect to the substrate. The cover plate CP of the substrate W (orthe sensor TIS) may be moved using an actuator in conjunction with atimetable or using a sensor indicating where the immersion space isrelative to the substrate table. The gaps need only to be minimized atthe time the immersion space is above that part of the substrate table.A gas knife clears the surface of the substrate table of liquid betweenexposures to immersion liquid, and thereby contributes to the risk ofgas bubbles when the surface is re-immersed. Because the gas knife driesthe entire surface of the substrate table, the gaps cannot be pre-filledwith liquid before coming into contact with the immersion space.

Alternatively, to minimize the number of gaps, a sensor TIS and/or thesubstrate W may share a hole in the substrate table WT.

One way to minimize the size of the gap required for the placement of anobject in or on the substrate table is to have the sensor TIS (or thesubstrate W or any other object in or on the substrate table) shapedwith a slanted (e.g., conical) edge that matches a slanted (e.g.,conical) surface of the hole in the substrate table WT. This is shown inFIG. 7. Less of a gap is required because the sensor TIS is effectivelyself-centering. This provides less surface area and less of a trap forbubbles. Using a self-centering sensor may give rise to a height steprather than a gap. The lithographic apparatus would then be adapted tobe able to take a height step into account during a scan of thesubstrate table.

An alternative method is also to use a membrane as part of a cover platethat bridges the gap between a substrate table and a substrate or asensor or any other object in or on the substrate table. This membranemay comprise a sticker. The sticker may be any suitable thickness aslong as it fits between the substrate table and the projection system,e.g., 5 to 50 microns.

One example of the use of a sticker is with a closing plate. The groovearound a closing plate that is used between substrate swaps is prone tocontaining bubbles because the closing plate is lowered onto thesubstrate table once the substrate has been replaced and then placedunder the immersion system to keep the immersion liquid sealed. Movementof walls of the immersion system in this way is a prominent reason forbubble formation. Therefore, the top surface of the closing plate CLDmay be extended as shown in FIG. 9 b with a projection so that the uppersurface 20 covers any groove around the part of the closing plate thatactually sits within the substrate table. Because the hole in thesubstrate table is sealed by the extended upper surface of the closingplate, the closing plate may be held in the substrate table using avacuum, and so the problem of bubbles is reduced or eliminated. In anembodiment, the extended surface 20 may be a thin circular layer that ismade from a solid piece of glass made by etching, or a sticker on theclosing plate. The sticker may be 10 to 20 μm so that the height stepdoes not cause a problem for the immersion system. The closing plate canthen be released by applying a pulse of pressurized gas under theextended surface.

The sticker may be used to cover a gap between the substrate and thecover plate. It may be made of glass, metal or plastic or any othersuitable unreactive substance. The sticker may be fixed with adhesive, athin film of liquid, or suction caused by a vacuum. Alternatively, itmay be an integral part of the substrate or the cover plate (or thesensor or closing plate).

Turning to FIG. 10, the problem of droplets D of liquid on the surfaceof the substrate causing gas bubbles is shown (and described earlier).There are several ways to deal with the droplets D on the substrate.

One method is to have substrate table moving more slowly with respect tothe immersion system so that the liquid front F is at less of an anglewith respect to the substrate W and there is less space for gas to betrapped between the droplet D and the liquid front F.

Alternatively or additionally, the shape of the droplet D may be changedso that the angle between the droplet D and the substrate W is lessacute so that less gas is trapped between the two liquid surfaces D andF. One way to do this is to make the surface of the substrate moreliquidphilic so that the surface of the droplet D is closer toperpendicular or even at an obtuse angle to the substrate, rather thanat an acute angle wherein gas may be trapped.

As mentioned above, liquid droplets D may be created on the substratesurface from the gas knife directing the gas into a gap between thesubstrate and the substrate table, thus causing liquid to “splash out”onto the substrate surface and the substrate table surface as shown inFIG. 11 a. In an embodiment, the gas knife may precede the liquid frontin a scan of the substrate surface and so liquid droplets may be createdjust before the liquid front of the immersion system reaches the samepoint on a substrate surface. This is shown by the direction of thearrow in FIG. 11 a.

One way to overcome this problem is shown in FIG. 11 b and is to scantowards the central part of the substrate rather than towards the edge.In FIG. 11 b, the substrate W and the substrate table WT are reversed inposition so that the scanning occurs from the edge of the substrate Wtoward its central part. Because of the direction of movement ofsubstrate with respect to the gas knife, as the edge of substrate passesunder the gas knife, the droplets that do spray onto the surface of thesubstrate are pushed forward by the gas knife. Those droplets D are not,in this embodiment, blown into the path of the liquid front F, but theyare effectively blown ahead of the liquid front F by the gas knife asshown by the arrow overlapping the droplets D in FIG. 11 b.

Bubbles may mostly occur on or near the dies nearest the edge of thesubstrate. The above-described adaptation to the scanning direction maybe further improved by first exposing all inner dies of the substrate W.The outer dies are subsequently exposed. In this way, by choosing a“long” exposure routing for exposing the edge dies, bubbles created bygoing back and forth over the substrate edge are given maximum time toescape before exposure. This method may be useful for reducing thenumber of bubbles that occur at the edge of a substrate.

Another possible solution to the problem of spraying liquid dropletsfrom a gap between the substrate and the substrate table is to ensurethat no liquid is left in the gap, for example by ensuring the drainflow is efficient. However, this runs the risk of gas being trapped inthe gap and floating up into the immersion system as described earlier.Refilling of the gap may be required between the gas knife and theliquid front.

Minimizing the distance between the liquid front and the gas knife inthe immersion system may still cause bubbles to be created, but onlyover a short distance near the very edge of the substrate, thus possiblyreducing errors on a greater part of the substrate.

By reference to a sensor herein, it is understood that this may includea transmission image sensor (TIS), a spot sensor, an integrated lensinterferometer sensor (ILIAS), and/or a slit sensor and may include asensor that comprises more than one detector. For example, a TIS mayinclude eight detectors, which may be covered by a cover plate eitherall together or individually. These sensors may be used to measure imagelocation, radiation dose, aberrations, polarization, and/or other imagequality parameters as well as or alternatively to align the substrate.

In these ways, errors caused by bubbles such as minimum dose errors anddistortions or blank spots on the exposed substrate may be reduced.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a radiation beam through a liquid onto a substrate,the apparatus comprising a support table configured to hold an object,the object comprising (i) a sensor, or (ii) a substrate, or (iii) aclosing plate, or (iv) a cover plate or (v) any combination of (i)-(iv),wherein a gap between the object and the support table is kept to aminimum in order to minimize bubble formation in the liquid.

In an embodiment, the gap between the object and the support table isless than 0.8 mm. In an embodiment, the gap between the object and thesupport table is less than 0.3 mm. In an embodiment, the apparatuscomprises a single cover plate used to cover a plurality of sensors inor on the support table. In an embodiment, the apparatus comprises acover plate that is transparent to the radiation beam. In an embodiment,the cover plate is a pellicle. In an embodiment, the pellicle isconnected on an outer edge of the support table. In an embodiment, thecover plate is integrated with a sensor. In an embodiment, the coverplate is made of quartz. In an embodiment, the apparatus furthercomprises an actuator configured to move the object laterally in a holein the support table in order to reduce, when in contact with theliquid, the gap between an edge of the object and a side of the hole. Inan embodiment, the actuator is configured to carry out lateral movementof the object within the support table in dependence on a position ofthe support table with respect to the liquid such that the part of thesupport table in contact with the liquid contains the smallest possiblegap size. In an embodiment, the support table comprises a holeconfigured to hold at least two objects therein so as to have a commongap between the objects and an edge of the hole, thus reducing a totalgap area on the support table. In an embodiment, the object comprises aslanted surface and the support table comprises a hole, in which theobject is to be positioned, with a corresponding slanted surface toallow self-centering of the object in the hole. In an embodiment, theslanted edge is a conical surface and the hole is a conical hole. In anembodiment, the apparatus further comprises a cover plate to cover theobject, the cover plate being segmented such that the segments areconfigured to slide over each other and cover a gap between the objectand the support table, such that the gap is effectively reduced to nogap. In an embodiment, the apparatus further comprises a cover plate tocover the object, the cover plate being made of elastic material suchthat it is configured to stretch over the object and cover a gap betweenthe object and the support table, such that the gap is effectivelyreduced to no gap. In an embodiment, the cover plate comprises a holethat is stretchable and through which the object may be inserted into ahole in the support table. In an embodiment, the apparatus furthercomprises a sticker configured to cover the gap, the sticker beingadhered in use of the apparatus to, or an integral part of, the supporttable, the object, or both the support table and the object on eitherside of the gap, the adhering being one of a thin film of liquid orsuction caused by a low pressure. In an embodiment, the sticker is madeof a thin layer of glass, metal, plastic, or any other suitableunreactive substance.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a radiation beam, through a liquid, onto asubstrate, the apparatus comprising: a support table configured to holdan object, the object comprising (i) a sensor, or (ii) a substrate, or(iii) a closing plate, or (iv) a cover plate or (v) any combination of(i)-(iv); and a sticker configured to cover a gap between the object andthe support table, the sticker being made of glass, metal, plastic orany other unreactive substance and adhered, in use of the apparatus, tothe object, the support table, or both, by a liquid or a low pressure.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-20. (canceled)
 21. A device manufacturing method, comprising:supplying a liquid between an object and a final optical element of aprojection system of a lithographic projection apparatus, wherein thelithographic projection apparatus comprises a movable table and theobject comprises at least one selected from the following: a sensor, asubstrate, a closing plate or other object in or on the movable table,and wherein a cover plate contacts the object and a top surface of themovable table and bridges a gap between the object and the top surfaceof the movable table, the cover plate being stretchable and having ahole in its interior; and projecting a radiation beam, through theliquid, onto a radiation-sensitive surface of a substrate.
 22. Themethod of claim 21, wherein the cover plate has a thickness selectedfrom the range of 5 to 50 microns.
 23. The method of claim 21, whereinthe cover plate comprises an adhesive to adhere the cover plate to theobject, the movable table, or both.
 24. The method of claim 21, whereinthe cover plate comprises plastic.
 25. The method of claim 21, whereinthe cover plate comprises metal.
 26. The method of claim 21, wherein theobject is a substrate having a radiation-sensitive material layer. 27.The method of claim 21, further comprising moving the cover plate withrespect to the object and the movable table.
 28. A device manufacturingmethod, comprising: supplying a liquid between an object and a finaloptical element of a projection system of a lithographic projectionapparatus, wherein the lithographic projection apparatus comprises amovable table and the object comprises at least one selected from thefollowing: a sensor, a substrate, a closing plate or other object in oron the movable table, wherein a cover plate contacts the object and atop surface of the movable table and bridges a gap between the objectand the top surface of the movable table, the cover plate having atleast two portions at partially separable from and movable with respectto each other; and projecting a radiation beam, through the liquid, ontoa radiation-sensitive surface of a substrate.
 29. The method of claim28, wherein the at least two portions are segments, such that the coverplate is segmented, the segments being moveable with respect to eachother to cover the gap.
 30. The method of claim 29, wherein the segmentsare movable over each other.
 31. The method of claim 28, wherein theobject comprises a sensor.
 32. The method of claim 28, comprising movingthe cover plate, using an actuator, with respect to the object and themovable table.
 33. The method of claim 28, wherein the object is asubstrate having a radiation-sensitive material layer.
 34. Amanufacturing method in a lithographic projection apparatus comprising afinal optical element of a projection system and a movable table, themethod comprising: moving an object comprising at least one selectedfrom the following: a sensor, a substrate, a closing plate or otherobject for in or on the movable table of the lithographic projectionapparatus, into a recess of the movable table, the object comprising acover plate that extends laterally from the object, wherein the movementof the object into the recess causes the cover plate to come intocontact with a top surface of the movable table and bridge a gap betweenthe object and the top surface of the movable table; supplying a liquidbetween the object and the final optical element; and projecting aradiation beam, through the liquid, onto a radiation-sensitive surfaceof a substrate.
 35. The method of claim 34, wherein the cover plate hasa thickness selected from the range of 5 to 50 microns.
 36. The methodof claim 34, wherein the object is a substrate having aradiation-sensitive material layer.
 37. The method of claim 34, whereinthe object is a sensor.
 38. The method of claim 34, wherein the coverplate comprises an adhesive to adhere the cover plate to the object, themovable table, or both.
 39. The method of claim 34, wherein the coverplate comprises plastic.
 40. The method of claim 34, wherein the coverplate comprises metal.